1. Field of the Invention
This invention relates to solar energy absorbing apparatus and more particularly to an improved apparatus and method for absorbing solar energy in a fluid while minimizing heat losses therefrom.
2. The Prior Art
Recent adverse events in the field of energy, particularly those events related to fossil fuels (i.e., petroleum and coal resources) has focused attention on the possibility of utilizing solar energy as an energy source. Solar energy is clean and, in many parts of the world, abundantly available during daylight hours.
Conventional solar energy collectors involve large absorbing panels through which a fluid is passed. However, these devices are, historically, relatively inefficient since a large percentage of the solar energy initially absorbed by the fluid is lost through conduction, convection, and reradiation to the surrounding ambient.
Attempts to minimize these losses by enclosing the absorber panel in a sealed envelope with a transparent upper panel and under a partial vacuum have proven difficult since the pressure differential between the atmospheric pressure of the surrounding ambient and the partial vacuum creates excessive tensile stresses in the periphery of the transparent panel resulting in fracture of the same. Attempts to overcome this problem by increasing the thickness of the transparent panel results in a corresponding increase in the weight, cost, and solar energy absorption characteristics of the transparent panel portion of the apparatus thereby offsetting most gains obtained by the use of a partial vacuum.
It would, therefore, be an advancement in the art to provide an apparatus and method for increasing the structural integrity of the transparent upper panel for an envelope in which a solar energy absorbing panel is isolated under partial vacuum while minimizing the conductive, convective and radiation heat losses from the absorber panel. Advantageously, it would be an advancement in the art to impart a constrictive force to the periphery of the upper, transparent panel to compensate for the tensile forces imposed by the pressure differential created by the internal vacuum in the envelope. It would be an even further advancement to utilize the stresses imposed by the pressure differential between the internal partial vacuum and the external atmospheric pressure to impose a constrictive force to the periphery of the transparent panel to thereby compensate for the tensile stresses therein. Such an apparatus and method is disclosed herein.